FISHERY BULLETIN; VOL. 69, NO. 2 



In a comprehensive treatment of oceanograph- 

 ic survey data taken in 1955-58, Tully, Dodimead, 

 and Tabata (1960) found the warm coastal 

 anomaly of 1957-58 to be associated with in- 

 creasing transport into the Alaska Gyre. They 

 describe this condition in terms of a south- 

 ward shift of the point of separation of flow 

 from the West Wind Drift. From their study 

 of the djTiamic topography, they inferred that 

 prior to the shift, in 1955 and 1956, most of the 

 water approaching the coast south of lat 45° N 

 entered the California Current. The fact that 

 negative anomalies prevailed along the coastal 

 zone in the latter half of 1955 and, to a lesser 

 extent, in 1956 suggests that the point of sep- 

 aration in this period was farther north than 

 usual. 



Whether the partition of the West Wind Drift 

 is influenced by upstream perturbations in the 

 zonal flow structure cannot be established with 

 certainty from the available survey data. The 

 geopotential topography as presented by Dodi- 

 mead, Favorite, and Hirano (1963) for the years 

 1955-59 does not reveal conclusive evidence of 

 upstream wave structure. The physical evi- 

 dence is limited to the anomalous characteristics 

 of the surface temperature field which have al- 

 ready been discussed. 



Some added perspective might be gained by 

 looking briefly at the dynamic constraints ap- 

 plicable to a standing wave in the West Wind 

 Drift. The average eastward current speed, U, 

 for a wave of length L and lateral (north-south) 

 extent D is given by Panofsky (1956) as fol- 

 lows: 



U — C = 



2ncos<^L= 

 477-- £• 



ll + L'/D^ 



This expression reduces to the Rossby wave 

 equation for a uniform zonal stream on a ro- 

 tating planet when the value of D approaches 

 infinity. 



In order to evaluate the right side of the above 

 equation, we will assume dimensional similarity 

 between the inferred wave and areas enclosed 

 by the plus or minus 1° C anomaly contours for 

 those cases where we presume a causal relation 

 with the current structure. Estimates of the 

 wave length L and of the ratio L/D were de- 

 termined from rough measurements of the lon- 

 gitudinal and lateral extent of the warm cell 

 pre.sent from October 1961 to September 1962. 

 Excluding two extreme cases (April and July 

 1962) the longitudinal dimensions of the warm 

 cell ranged between about 800 (March 1962) 

 and 1600 (January 1962) nautical miles. The 

 corresponding ratios of longitudinal to lateral 

 extent for these particular cases were 1.3 and 

 2.0 respectively. Substitution of these values 

 for L and L/D in the wave equation yields 35 

 and 85 cm/sec (approximately) for average cur- 

 rent speed through a stationary wave. Of 

 course, the areas enclosed by the 1° C anomaly 

 contours presumably define only a portion of 

 the hypothetical wave, and to substitute the di- 

 mensions of these areas for L and D would 

 understate the theoretical current speed. 



Current speeds in the West Wind Drift, com- 

 puted from dynamic height anomalies, are gen- 

 erally less than 10 cm sec (Dodimead et al, 

 1963). Data from drift bottles (Dodimead and 

 Hollister, 1962) indicate current speeds up to 

 20 cm sec in the same region. Thus, the theo- 

 retically computed results are too high, but con- 

 sidering the approximations used they are not 

 altogether unreasonable. 



where C is the wave speed (zero for a standing 

 wave) 



<\> is the mean latitude 



n is the angular velocity of the earth 

 (7.292 X 10-^ sec-') 



E is the radius of the earth 

 (6.37 X 10« m). 



LITERATURE CITED 



Dodimead, A. J., and H. J. Hollister. 



1962. Canadian drift bottle releases and recoveries 

 in the North Pacific Ocean. Fish. Res. Bd. Can., 

 Manuscr. Rep. Ser. (Oceanogr. Limnol.) 141, 64 p. 

 (Processed.) 



Dodimead, A. J., F. Favorite, and T. Hirano. 



1963. .Salmon of the North Pacific Ocean. Part II. 

 Review of oceanography of the Subarctic Pacific 

 region. Int. N. Pac. Fish. Comm., Bull. 13, 195 p. 



354 



